Optical sheet, method for producing the same and display apparatus

ABSTRACT

A lens film with small warpage even when a transparent base is thin is provided. Pole prisms made of a hardening resin are arranged along the extending direction on a transparent base made of flexible material. The transparent base has a depression according to a valley between the pole prisms adjacent to each other. The pole prism has a sloping face extending to an inner wall of the he depression. The transparent base is in contact with the valley. A layer not functioning as a prism, that is, a so-called skirt layer does not exist between the transparent base and the pole prisms.

CROSS REFERENCES TO RELATED APPLICATIONS

The present invention contains subject matter related to Japanese PatentApplication JP 2006-129633 filed in the Japanese Patent Office on May 8,2006, and Japanese Patent Application JP 2006-240839 filed in theJapanese Patent Office on Sep. 5, 2006, the entire contents of whichbeing incorporated herein by references.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical sheet having convex shape onthe surface, a method for producing it, and a display apparatusincluding the optical sheet.

2. Description of the Related Art

In these years, cathode ray tubes (CRT), which were a mainstream ofdisplay apparatuses in the past, have been replaced by liquid crystaldisplay apparatuses, since the liquid crystal display apparatuses haveadvantages such as low electrical power consumption, space-savingfeature, and low cost.

There are several types of the liquid crystal display apparatuses whencategorized by, for example, illumination methods in displaying images.As a representative example, a transmissive display apparatus whichdisplays images by utilizing a light source arranged behind a liquidcrystal panel can be cited.

In mobile products driven by a battery including such a displayapparatus, the electrical power consumption of the display apparatus isenormously large, which is an obstacle to extend battery life.Specially, the ratio of the electrical power consumption of thebacklight used in the display apparatuses is enormously large.Therefore, by reducing the electrical power consumption as much aspossible, the battery life can be extended. In the result, practicalvalues of the mobile products can be improved. However, it is notpreferable that the electrical power consumption of the backlight issimply reduced, since luminance of the backlight is largely lowered, andthereby visibility of screen display of the display apparatus becomesunfavorable. Therefore, some measures to reduce the electrical powerconsumption of the backlight without largely lowering the luminance ofthe backlight have been proposed.

For example, in Japanese Unexamined Utility Model ApplicationPublication No. 3-69184, a measure that an optical sheet having aplurality of pole prisms on the surface is arranged between a liquidcrystal panel and a light source has been disclosed. A description willbe specifically given of the optical sheet by using FIG. 12 and FIG. 13.

FIG. 12 shows an example of a cross sectional structure of atransmissive display apparatus 100 including lens films 112 and 113 asthe foregoing optical sheet. FIG. 13 shows an enlarged view of part of across section of the lens film 112. The display apparatus 100 mainlyincludes a liquid crystal panel 120 and an illumination system 110(so-called backlight) arranged behind the liquid crystal panel 120 (thatis, opposite side of an observer side).

The illumination system 110 includes a light source 111, the lens films112 and 113, a diffusion sheet 114, a lamp reflector 115, an light guideplate 116, and a reflecting sheet 117. The liquid crystal panel 120mainly includes a polarizing plate 121, a transparent substrate 122, acolor filter 123, a transparent electrode 124, an orientation film 125,a liquid crystal layer 126, an orientation film 127, a transparent pixelelectrode 128, a transparent substrate 129, and a polarizing plate 130in this order from the observer side.

In the display apparatus 100, light emitted from the light source 111 isreflected by the lamp reflector 115 and the reflecting sheet 117,directed in the direction of the liquid crystal panel 120, spread overthe whole area of the liquid crystal panel 120 by the light guide plate116, evenly diffused by the diffusion sheet 114, condensed by the lensfilms 112 and 113, and emitted to the liquid crystal panel 120. Thelight entering the liquid crystal panel 120 is transmitted to theobserver side according to a size of a voltage applied to each pixel bya not-shown drive circuit.

As above, by arranging the lens films 112 and 113 between the liquidcrystal panel 120 and the diffusion sheet 114, light emitted from thelight source 111 can efficiently enter the liquid crystal panel 120. Inthe result, the electrical power consumption of the backlight can bereduced without largely lowering luminance of the backlight.

For example, as described in Japanese Unexamined Patent ApplicationPublication Nos. 4-356746, 5-314545, 5-325272, and 6-47806, the lensfilms 112 and 113 can be produced by coating a transparent base with anuncured hardening resin, pressing a mother die having a reversal shapeof pole prisms onto the hardening resin, and curing the hardening resinin such a state to transcribe the pole prism shape.

SUMMARY OF THE INVENTION

However, in the lens film obtained by the foregoing manufacturingmethod, the lens film is largely warped to the hardening resin side dueto shrinkage due to curing of the hardening resin. In particular, whenthe transparent base is thin, strength of the transparent base islowered, and a ratio of shrinkage due to curing of the hardening resinis increased. In the result, the optical sheet is significantly warpedto the hardening resin side. Even when large warpage is generated in thelens film as above, it is possible to press the warpage to arrange thelens film in the display apparatus. However, after the lens film isarranged in the display apparatus, the lens film is in contact withother optical parts in adjacent thereto in part due to the warpage.Therefore, there has been a disadvantage that Newton rings, flaws andthe like are thereby generated, and the display quality of the displayapparatus is lowered.

In view of the foregoing problem, in the present invention, it isdesirable to provide an optical sheet with small warpage even in thecase of a thin transparent base, a method for producing the opticalsheet, and a display apparatus including the optical sheet.

An optical sheet of an embodiment of the invention is the one in whichpole prisms made of a hardening resin are arranged along an extendingdirection on a transparent base made of a flexible material. Here, thetransparent base is in contact with a valley between the pole prismsadjacent to each other. A display apparatus of an embodiment of theinvention is the one including a panel, a light source emitting lightfor illuminating the panel, and one or a plurality of the optical sheetsprovided between the panel and the light source.

In the optical sheet and the display apparatus of the embodiment of theinvention, the transparent base is in contact with the valley betweenthe pole prisms adjacent to each other. Therefore, a layer notfunctioning as a prism, that is, a so-called skirt layer does not existbetween the transparent base and the pole prism. Here, the expression“skirt layer does not exist” is a concept including a case that no skirtlayer exists and a case that the skirt layer remains slightly (forexample, 0.28 μm or less) due to an error in manufacturing or the like.Thereby, the height of the pole prism from the surface of thetransparent base becomes the bare minimum, and a volume of the hardeningresin becomes smaller than a case that the skirt layer exists. Further,since no skirt layer exists, there is almost no portion where theadjacent pole prisms are in contact with each other.

According to an embodiment of the invention, there is provided a methodfor producing an optical sheet including the following steps A to D:

A: a step of arranging an uncured hardening resin on a transparent basemade of a flexible material;

B: a step of pressing a mother die having projections onto the hardeningresin, and pressing tops of the projections onto the transparent baseuntil the tops of the projections are in contact with the transparentbase;

C: a step of forming the hardening resin by curing the hardening resinin a state that the projections are pressed onto the transparent base;and

D: a step of peeling the formed hardening resin from the mother dietogether with the transparent base.

In the method for producing an optical sheet of the embodiment of theinvention, not only the projections of the mother die are pressed ontothe hardening resin, but also the projections are pressed onto thetransparent base. Therefore, a layer not functioning as a prism, thatis, a so-called skirt layer does not exist between the transparent baseand the pole prism. Thereby, the height of the pole prism from thesurface of the transparent base becomes the bare minimum, and a volumeof the hardening resin becomes smaller than the case that the skirtlayer exists. Further, since no skirt layer exists, there is almost noportion where the adjacent pole prisms are in contact with each other.

According to the optical sheet, the method for producing the same, andthe display apparatus of the embodiment of the invention, there is noskirt layer between the transparent base and the pole prism. Therefore,the volume of the hardening resin becomes smaller than the case that theskirt layer exists. Thereby, warpage of the optical sheet caused byshrinkage due to curing of the hardening resin can be largely decreased.Further, since there is almost no portion where the adjacent pole prismsare in contact with each other, strain caused by shrinkage due to thecuring of the hardening resin is not organically bonded. Thereby, almostall warpages of the optical sheet can be eliminated. As a result, evenin a case of having the transparent base thin, the optical sheet withsmall warpage can be realized. By arranging such an optical sheet withsmall warpage in the display apparatus, there is no possibility thatNewton rings, flaws and the like are generated, and the display qualityof the display apparatus can be improved.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section showing an example of a structure of a displayapparatus of an embodiment of the invention;

FIG. 2A is a cross section showing an example of a structure of anupper-side lens film;

FIG. 2B is a cross section showing an example of a structure of alower-side lens film;

FIG. 3A is a cross section showing an example of another structure ofthe upper-side lens film;

FIG. 3B is a cross section showing an example of another structure ofthe lower-side lens film;

FIG. 4 is a model view showing an example of a structure of a lens filmmanufacturing apparatus;

FIG. 5 is a cross section for explaining an example of operations of atranscriptional machinery of FIG. 4;

FIG. 6 is a cross section for explaining an example of operations ofanother transcriptional machinery of FIG. 4;

FIGS. 7A and 7B are model views for explaining forms of warpage of thelens film;

FIG. 8 is a model view showing an example of measurement method ofamount of warpage of the lens film;

FIG. 9 is a cross sectional photograph of the lens film;

FIG. 10 is a relational view for explaining a relation between a depthof a depression or a thickness of a skirt layer and an amount ofwarpage;

FIG. 11 is a model view showing an example of a measurement method of arelative luminance ratio of the lens film;

FIG. 12 is a cross section showing an example of a structure of adisplay apparatus of the related art; and

FIG. 13 is a cross section showing an example of a structure of a lensfilm of FIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the invention will be hereinafter described in detailwith reference to the drawings.

FIG. 1 shows a cross sectional structure of a display apparatus 1 of anembodiment of the invention. The display apparatus 1 is a transmissivedisplay apparatus for displaying an image by active matrix drive. Thedisplay apparatus 1 includes a liquid crystal panel 20 and anillumination system 10 arranged behind the liquid crystal panel 20.

The liquid crystal panel 20 has a laminated structure having a liquidcrystal layer 26 between a transparent substrate 22 on an observer sideand a transparent substrate 29 on the illumination system 10 side.Specifically, the liquid crystal panel 20 has a polarizing plate 21, thetransparent substrate 22, a color filter 23, a transparent electrode 24,an orientation film 25, the liquid crystal layer 26, an orientation film27, a transparent pixel electrode 28, a transparent substrate 29, apolarizing plate 30, and a diffusion sheet 31 in this order from theobserver side.

The polarizing plates 21 and 30 are a kind of optical shutter, and letthrough only light (polarization) in a certain oscillation direction.The polarizing plates 21 and 30 are respectively arranged so that thepolarizing axes are different from each other by 90 deg. Thereby, lightemitted from the illumination system 10 is transmitted through orblocked by the liquid crystal layer 26.

The transparent substrates 22 and 29 are made of a substrate transparentto visible light such as a plate glass. Though not shown, on thetransparent substrate 29 on the illumination system 10 side, an activedrive circuit including a TFT (Thin Film Transistor) as a drive deviceelectrically connected to the transparent pixel electrode 28, wiring andthe like is formed.

In the color filter 23, color filters for respectively color-separatinglight emitted from the illumination system 10 into three primary colorsof red (R), green (G), and blue (B) are arranged.

The transparent electrode 24 is made of, for example, ITO (Indium TinOxide), and functions as a common opposed electrode.

The orientation films 25 and 27 are made of, for example, a polymermaterial such as polyimide, and perform orientation for the liquidcrystal.

The liquid crystal layer 26 is made of, for example, VA (VerticalAlignment) mode liquid crystal, TN (Twisted Nematic) mode liquidcrystal, or STN (Super Twisted Nematic) mode liquid crystal. The liquidcrystal layer 26 has a function to transmit or block light emitted fromthe illumination system 10 for every pixel by a voltage applied from anot-shown drive circuit.

The transparent pixel electrode 28 is made of, for example, ITO, andfunctions as an electrode for each pixel.

The diffusion sheet 31 has a function to diffuse light emitted from theillumination system 10 in the same manner as a diffusion sheet 14(described later), and decrease light unevenness. The diffusion sheet 31is provided according to needs.

The illumination system 10 has: a lamination structure in which lensfilms 12A and 13A (optical sheet), a diffusion sheet 14, a light guideplate 16, and a reflecting sheet 17 are layered in the order from theobserver side; a light source 11 arranged on the side face of thelamination structure; and a lamp reflector 15 arranged around the lightsource 11. Part of the lamp reflector 15 is opened toward the laminatedstructure. As above, the illumination system 10 has a so-callededge-light structure.

The light source 11 is formed of a cold cathode fluorescent lamp calledCCFL, a light emitting diode (LED) or the like.

The lamp reflector 15 has a function to reflect part of light emittedfrom the light source 11 in the direction of the light guide plate 16.Thereby, light emitted from the light source 11 can be effectivelyutilized.

The light guide plate 16 has a function to totally reflect andconcurrently propagate light emitted from the light source 11, and tospread the light over the whole area of the liquid crystal panel 20.Thereby, light emitted from the light source 11 can become flat light.

The reflecting sheet 17 has a function to reflect light to be leakedfrom the light guide plate 16 toward inside of the light guide plate 16.Thereby, as with the foregoing lamp reflector 15, light emitted from thelight source 11 can be effectively utilized.

The diffusion sheet 14 has a function to diffuse flat light spread overthe whole area of the liquid crystal panel 20 by the light guide plate16 and to decrease light unevenness. Thereby, the whole area of theliquid crystal panel 20 is illuminated with light with uniformbrightness.

The lens films 12A and 13A are, for example, as shown in enlarged viewsthereof in part in FIGS. 2A and 2B, respectively structured in a mannerthat pole prisms 12A2 (13A2) having triangle pole shape are arranged ona transparent base 12A1 (13A1) in the extending direction. Astripe-shaped valley 12A3 (13A3) with a depth D1 is provided between theadjacent pole prisms 12A2 (13A2). The pole prism 12A2 (13A2) has asloping face 12A4 (13A4) extending to the surface of the transparentbase 12A1 (13A1). The pole prism 12A2 and the pole prism 13A2 arearranged so that respective extending directions cross each other (forexample, cross each other by 90 deg) and have a function to align anddirect light direction in the direction of the liquid crystal panel 20.

Here, the transparent base 12A1 (13A1) is a transparent resin sheet witha thickness D2 made of a flexible material. The valley 12A3 (13A3) is incontact with the plane surface of the transparent base 12A1 (13A1). Thatis, no skirt layer exists between the transparent base 12A1 (13A1) andthe pole prism 12A2 (13A2). Here, “no skirt layer exists” includes acase that no skirt layer exists and a case that a skirt layer remainsslightly (for example, under 0.28 μm) due to an error in manufacturingor the like. That is, a thickness ΔDy of the skirt layer is totally 0 oran extremely small value. A distance D3 between a bottom face and a topof the pole prism 12A2 (13A2) (that is, a height of the pole prism 12A2(13A2)) is totally equal to or almost equal to the depth D1 of thevalley 12A3 (13A3).

Instead of the transparent base 12A1 (13A1), as shown in FIGS. 3A and3B, it is possible to provide a transparent base 12B1 (13B1) havingdepressions 12B5 (13B5) with a depth ΔDx (D1-D3) cyclically and having aconvex curved face 12B6 (13B6) between the adjacent depressions 12B5(13B5). However, in this case, a pole prism 12B2 (13B2) having a slopeface 12B4 (13B4) extending to the inner wall of the depression 12B5(13B5) of the transparent base 12B1 (13B1) and contacting with thesurface of the transparent base 12B1 (13B1), and having a concave curvedface contacting with the convex curved face 12B6 (13B6) on thetransparent base 12B1 (13B1) side is provided on the transparent base12B1 (13B1). There is no gap between the transparent base 12B1 (13B1)and the pole prism 12B2 (13B2). Therefore, a lens film 12B (13B) havingthe pole prism 12B2 (13B2) on the transparent base 12B1(13B1) includesno skirt layer. Here, the distance D3 between the concave curved face ofthe pole prism 12B2 (13B2) and the top (that is, a height of the poleprism 12B2 (13B2)) is smaller than the depth D1 of the trough 12B3(13B3).

For simplifying descriptions, the transparent bases 12A1 (13A1), 12B1(13B1) will be hereinafter generically named the transparent base 12A1or the like. Other elements will be also hereinafter generically namedin the same manner.

For the foregoing flexible material, a material having resistance ortransmittance to energy used for forming the pole prism 12A2 or the likein the manufacturing process can be cited. For example, when the poleprism 12A2 or the like is formed by using active energy lines such as anultraviolet ray and an electron ray, materials which transmit the activeenergy lines, for example, a polyester resin, an acrylic resin, apolycarbonate resin, a vinyl chloride resin, a polymethacrylic imideresin are preferable.

The pole prism 12A2 or the like is made of a hardening resin which iscured by heating or irradiating active energy lines such as anultraviolet ray and an electron ray. As a hardening resin, for example,polyesters, an epoxy resin, a (meta)acrylate resin such aspolyester(meta)acrylate, epoxy(meta)acrylate, and urethane(meta)acrylatecan be cited. The (meta)acrylate resin is preferable since the(meta)acrylate resin has favorable optical characteristics. Further, asa main component of the hardening resin, a polymerization initiator bythe active energy lines such as polyacrylate is preferably contained. Inthe case that the convex curved face 12B6 (13B6) is provided on thesurface of the transparent base 12B1 (13B1) (refer to FIGS. 3A and 3B),when a refractive index of the foregoing hardening resin is smaller thanthat of the flexible material forming the transparent base 12A1 or thelike, the convex curved face 12B6 (13B6) on the surface of thetransparent base 12B1 (13B1) can function as a condenser.

Next, a description will be given of an example of a method of formingthe lens film 12A or the like with reference to FIGS. 4 to 6. First, adescription will be given of a lens film manufacturing apparatus 30 usedfor forming the lens film 12A or the like.

FIG. 4 shows a schematic structure of the lens film manufacturingapparatus 30. FIG. 5 shows an enlarged view of an example of a crosssectional structure in forming the lens film 12A (13A) by atranscriptional machinery 35 of FIG. 4. FIG. 6 is an enlarged view of anexample of a cross sectional structure in forming the lens film 12B(13B) by the transcriptional machinery 35 of FIG. 4. In FIG. 4, ahardening resin P is not shown.

The lens film manufacturing apparatus 30 includes an unwinding device 31for supplying a transparent base S, a speed adjustment device 32 foradjusting feed speed of the transparent base S supplied from theunwinding device 31, a resin supply device 33 for dropping the uncuredhardening resin P on the transparent base S, a film thickness adjustmentdevice 34 for adjusting a thickness of the hardening resin P dropped onthe transparent base S, a transcriptional machinery 35 for transcribinga prism shape on the hardening resin P to form the lens film 12A or thelike, a mold-releasing device 36 for demolding the lens film 12A or thelike from the transcriptional machinery 35, and a winding device 37 forwinding the lens film 12A or the like.

Here, the transcriptional machinery 35 has pressure rolls 35A and 35Bwhich rotate centering on rotational axis X, a forming roll 35C whichrotates centering on rotational axis Y parallel to the rotational axisX, and a light source 35D provided between the pressure rolls 35A and35B.

The pressure roll 35A feeds the transparent base S to the light source35D side while pressing the transparent base S coated with the hardeningresin P with a given thickness by a given pressure from the transparentbase S side in the direction of the forming roll 35C. The pressure roll35B feeds the transparent base S from the light source 35D side to themold-releasing device 36 side while pressing the transparent base Shaving the hardening resin P formed in a given shape on the surfacethereof by a given pressure from the transparent base S side in thedirection of the forming roll 35C.

As shown in FIGS. 5 and 6, the forming roll 35C has a mother die inwhich pole projections 35C-1 with a reversal shape of the pole prism12A2 or the like are arranged on the peripheral face along the extendingdirection. Rotational radius R2 in the portion where the projection35C-1 is formed in the forming roll 35C (distance between the rotationalaxis Y of the forming roll 35C and a top 35C-2 of the projection 35C-1)is larger than rotational radius R1 in the portion where the projection35C-1 is not formed (distance between the rotational axis Y of theforming roll 35C and a surface 35C-3 where the projection 35C-1 is notformed). Thereby, when the projection 35C-1 is pressed onto thetransparent base S, there is no possibility that the surface 35C-3 notformed with the projection 35C-1 is in contact with the transparent baseS. Therefore, the top 35C-2 of the projection 35C-1 can be surelypressed onto the transparent base S. Therefore, in the transcriptionalmachinery 35, by appropriately adjusting a pressure with which the top35C-2 of the projection 35C-1 is pressed onto the transparent base S, astate that the top 35C-2 is in contact with the surface of thetransparent base S can be maintained. Further, it is also possible thatby pressing the top 35C-2 into the transparent base S, depressions and aconvex curved face between adjacent depressions are formed on thesurface of the transparent base S.

The light source 35D irradiates an active energy line L such as anultraviolet ray and an electron ray from the transparent base S side tothe hardening resin P pressed onto the forming roll 35C by the pressurerolls 35A and 35B.

When the foregoing lens film manufacturing apparatus 30 startsoperations, the transparent base S supplied from the unwinding device 31is adjusted to a given speed by the speed adjustment device 32, and theuncured hardening resin P is dropped on the transparent base S by theresin supply device 33. The dropped hardening resin P is adjusted to agiven thickness by the film thickness adjustment device 34. Thehardening resin P with the film thickness adjusted is put into thetranscriptional machinery 35 with the surface thereof facing to theforming roll 35B side. Then, the hardening resin P is pressed onto theforming roll 35B from the transparent base S side by the pressure rolls35A and 35B, and a shape of the pole prism 12A2 or the like istranscribed.

When the pole prism 12A2 (13A2) is formed, as shown in FIG. 5, pressureis applied by the pressure rolls 35A and 35B until the top 35C-2 of theprojection 35B-1 is in contact with the transparent base S. Thereby,there is almost no portion where the adjacent pole hardening resin P isin contact with each other. Meanwhile, when the pole prism 12B2 (13B2)is formed, as shown in FIG. 6, pressure is applied by the pressure rolls35A and 35B until the top 35C-2 of the projection 35B-1 is pressed intothe transparent base S. Thereby, there is almost no portion where theadjacent pole hardening resin P is in contact with each other. Inaddition, the depression 12B5 (13B5) is formed in the pressed portion,and the convex curved face 12B6 (13B6) is formed between the adjacentdepressions 12B5 (13B5).

Subsequently, light L emitted from the light source 35D is irradiated tothe hardening resin P through the transparent base 12A1 or the like in astate that the top 35C-2 of the projection 35B-1 is pressed onto thetransparent base 12A1 or the like. Thereby, a shape transcribed on thehardening resin P is fixed. In the result, the pole prism 12A2 (13A2) isformed on the transparent base 12A1 (13A1), and the pole prism 12B2(13B2) is formed on the transparent base 12B1 (13B1). After that, thetransparent base 12B1 or the like is released from the transcriptionalmachinery 35 by the mold-releasing device 36 together with the poleprism 12A2 or the like, and the released resultant is wound by thewinding device 37. As above, the lens film 12A or the like of thisembodiment is formed.

The deeper a depth ΔDx of the depression 12B5 (13B5) is, the smaller acurvature radius of the curved face 12B6 (13B6) can be. However, when apressure of the pressure rolls 35A and 35B is excessively increased todeepen the depression 12B5 (13B5), there is a possibility that thedepression 12B5 (13B5) in the transparent base 12B1 (13B1) becomeswhite, and thus a light transmittance decreases. Therefore, the depthΔDx of the depression 12B5 (13B5) is preferably a depth to an extentthat no whitening is caused at the transparent base 12B1 (13B1) (about10% or less of thickness D2 of the transparent base 12B1 (13B1)).

Next, basic operations in displaying an image in the display apparatus 1including the lens film 12A or the like formed as above will bedescribed.

First, in the illumination system 10, part of light emitted from thelight source 11 directly enters the light guide plate 16, and the restof light thereof is reflected by the lamp reflector 15 and then entersthe light guide plate 16. The light entering the light guide plate 16 isemitted from the top face of the light guide plate 16, evenly diffusedby the diffusion sheet 14, oriented by the lens film 12A13, and emittedto the liquid crystal panel 20.

In the liquid crystal panel 2, incident light from the illuminationsystem 10 is transmitted according to a size of a voltage applied forevery pixel between the transparent pixel electrode 28 and thetransparent electrode 24 as an opposed electrode, color-separated by thecolor filter 23, and emitted to the observer side. Thereby, color imagesare displayed.

Next, a description will be given of effects of the lens film 12A or thelike of this embodiment in comparison with the lens film 112 of relatedart shown in FIG. 13.

The lens film 112 of related art is different from the lens film 12A orthe like of this embodiment mainly in that the lens film 112 has a poleprism 112-2 on a transparent base 112-1 with a skirt layer 112-5 inbetween. As described above, the skirt layer 112-5 is a layer notfunctioning as a prism, which is not necessary in the optical design.However, in the past, when an uncured hardening resin is cured totranscribe a shape of the pole prism 112-2, the skirt layer 112-5 havinga uniform thickness is provided to prevent deterioration oftranscription characteristics caused by shrinkage due to curing of thehardening resin.

However, when such a skirt layer 112-5 is provided, a volume of theuncured hardening resin necessary for forming the pole prism 112-2 isnaturally increased, compared to a case in which no skirt layer 112-5 isprovided. Further, the adjacent pole prisms 112-2 are in contact witheach other with the skirt layer 112-5 in between, strain caused byshrinkage due to curing of the hardening resin is organically bonded.Therefore, shrinkage due to curing of the hardening resin becomes large.In the result, large warpage (warpage on the plus side) as shown in FIG.7B is generated in the lens film 112.

An amount of warpage can be, for example, measured by using a heightgauge 210 arranged on a level block 200 as shown in FIG. 8. The heightgauge 210 includes a scale 211 which extends in the directionperpendicular to the level block 210, a movable section 212 which isarranged movably and extends in the direction parallel to the levelblock 200, and a base 213 which is connected to an end of the scale 211and supports the scale 211. A measurement target 220 is placed with thesurface of the side warped in a state of a convex upward on the levelblock 200, the movable section 212 is quietly dropped from upward of themeasurement target 220, and a scale indicated in the scale 211 from aposition of the movable section 212 at a moment when the bottom face ofthe movable section 212 is in contact with the concave surface of themeasurement target 220 is read, and thereby measurement is performed. Asan apparatus allowing such measurement, for example, HD-30A of MITUTOYOcan be cited. When the surface on the side formed with a prism is warpedin a state of a convex as shown in FIG. 7A, it is described that beingwarped to the minus side. When the surface on the side opposite of theside formed with a prism (resin base side) is warped in a state of aconvex as shown in FIG. 7B, it is described that being warped to theplus side.

Even when large warpage is generated in the lens film 112 as above, itis possible to press the warpage and arrange the lens film 112 in thedisplay apparatus 1. However, when the lens film 112 is arranged in thedisplay apparatus 1, it is often the case that the lens film 112 ispartly in contact with other optical component (diffusion sheets 14 and31) or the like adjacent thereto due to the warpage, and thereby Newtonrings, flaws and the like are generated and the display quality of thedisplay apparatus 1 is lowered. Such an issue has been largely generatedparticularly in the case of mobile usage in which a gap in the displayapparatus 1 is slightly provided. Such a case has lead to lowering ofthe yield.

Meanwhile, the lens film 12A or the like of this embodiment is formed sothat the valley 12A3 or the like is in contact with the transparent base12A1 or the like by using the foregoing producing method. Thereby, theskirt layer regarded as a necessary component in the past is excluded,and a volume of the uncured hardening resin P necessary in forming thepole prism 12A2 or the like is reduced. In the result, shrinkage due tocuring of the hardening resin P largely decreases. Further, since thereis almost no portion where the adjacent pole prisms 12A2 or the like arein contact with each other, strain caused by shrinkage due to the curingof the hardening resin P is not organically bonded. Thereby, almost allwarpages of the lens film 12A or the like can be eliminated.

Further, when the depression 12B5 (13B5) is formed by using theforegoing producing method, stress is generated in the directionopposite to the direction of stress due to shrinkage of the pole prism12B2 (13B2) in the vicinity of the depression 12B5 (13B5) of thetransparent base 12B1 (13B1). In the result, an amount of warpagegenerated by the lens film 12B largely decreases. Therefore, there is nopossibility that Newton rings, flaws or the like are generated, and thedisplay quality of the display apparatus 1 is significantly favorable.

In the foregoing producing method, it has been confirmed that intranscribing a shape of the pole prism 12A2 or the like by curing theuncured hardening resin P, there is no possibility that transcriptioncharacteristics are not deteriorated by shrinkage due to curing of thehardening resin P even when no skirt layer is provided (refer to a crosssectional photograph of FIG. 9). Therefore, there is no possibility thatthe display quality of the display apparatus 1 is deteriorated even whenno skirt layer is provided.

Further, in this embodiment, when the depression 12B5 (13B5) is formedon the surface of the transparent base 12B1 (13B1), the convex curvedface 12B6 (13B6) is formed between each depression 12B5 (13B5)accordingly. Therefore, by making the curved face 12B6 (13B6) functionas a condenser, front luminance can be improved.

In the field of mobile devices, display apparatuses are desired tobecome thinner. Each component composing the display apparatuses aredemanded to become thinner as long as possible. A description will begiven thereof with reference to FIG. 13. To make the lens film 112thinner, for example, the transparent base 112-1 of the lens film 112may be made thin. However, when the transparent base 112-1 is made thin,strength of the transparent base 112-1 is lowered, and a rate ofshrinkage due to curing of a hardening resin is increased. Therefore,the lens film 112 is significantly warped to the pole prism 112-2 side.Then, the depth D1 of the valley 112-3 of the pole prism 112-2 may bemade shallow instead of the transparent base 112-1. However, the depthD1 of the valley 112-3 is made simply shallow, a slope angle of theslope face 112-4 becomes small, and front luminance is lowered.Therefore, a pitch of the pole prism 112-2 should be decreased whilemaintaining the slope angle of the slope face 112-4 of the pole prism112-2. However, when the pitch of the pole prism 112-2 is excessivelydecreased, the front luminance is decreased in reality. As a result,utility of the lens film 112 provided for the purpose of improvingluminance is decreased. Therefore, it is found that in the case of FIG.13, to make the lens film 112 thinner without decreasing frontluminance, there are only the following methods. One method is toeliminate the skirt layer 112-5 located under the pole prism 112-2. Theother method is to make the transparent base 112-1 thin. However, in thepast, there is no idea to eliminate the skirt layer 112-5 since theskirt layer 112-5 is actively provided as described above. Meanwhile,when the transparent base 112-1 is made thin, large warpage isgenerated. Therefore, it has been necessary to make the transparent base112-1 thick to some degree (for example, about 50 μm).

Meanwhile, in the lens film 12A or the like of this embodiment, theskirt layer which has been regarded as a necessary component is activelyeliminated, the transparent base 12A1 or the like and the valley 12A3 orthe like are in contact with each other, and portions where the adjacenttriangle pole-shaped hardening resin are in contact with each other arealmost eliminated. Thereby, strain generated curing and shrinkage of theadjacent triangle pole-shaped hardening resin is not organically bonded.Therefore, warpage of the lens film 12A or the like can be almosteliminated.

In the result, even when the transparent base 12A1 or the like is madethin, there is no possibility that the lens film 12A or the like iswarped. Therefore, for example, it is possible that the whole thicknessof the lens film 12A or the like is made thin by making the transparentbase 12A1 or the like thin. Further, it is possible that front luminanceis increased almost without changing the whole thickness of the lensfilm 12A or the like by making the transparent base 12A1 or the likethin and making the pitch of the pole prism 12A2 or the like large.

EXAMPLES

Next, a description will be given of examples of the lens film 12A orthe like of this embodiment in comparison with the lens film 112 ofcomparative examples.

In the lens film 12A or the like according to the examples, the width(pitch) in the arrangement direction of the pole prism 12A2 or the likewas 31 μm, the depth D1 of the valley 12A3 or the like was 15 μm, theangle of the top (apex angle) of the pole prism 12A2 or the like was 90deg, and the thickness D2 of the transparent base 12A1 or the like was50 μm. In addition, the depth of the depression 12B5 (13B5) (−ΔDx(=D3−D1)) was −4.31 μm, −3.13 μm, −2.46 μm, −2.04 μm, −1.21 μm, −0.5 μm,+0.0 μm, or +0.25 μm (refer to Table 1). The depth (−ΔDx) of +0.0 μmmeans that no skirt layer exists. The depth (−ΔDx) of +0.25 μm meansthat the skirt layer slightly remains due to an error in manufacturingor the like, that is, means that the skirt layer does not existpractically.

Meanwhile, in the lens film 112 according to the comparative examples,as in the foregoing examples, the width (pitch) in the arrangementdirection of the pole prism 112-2 was 31 μm, the depth D1 of a valley112-3 was 15 μm, the angle of the top (apex angle) of the pole prism112-2 was 90 deg, and the thickness D2 of the transparent base 112-1 was50 μm. In addition, the thickness of the skirt layer 112-5 (ΔDy(=D3−D1)) was +0.5 μm, +6.5 μm, +17.5 μm, +25.5 μm, +34.5 μm (refer toTable 1).

TABLE 1 Thickness Amount Depth of of skirt of depression layer Pitchwarpage D2 D1 D3 H −ΔDx (μm) −ΔDy (μm) (μm) (mm) (μm) (μm) (μm) (μm)Example −4.31 — 31 0.0 50 15 10.69 60.5 Example −3.13 — 31 0.0 50 1511.87 61.8 Example −2.46 — 31 0.0 50 15 12.54 62.5 Example −2.04 — 310.0 50 15 12.96 63.0 Example −1.21 — 31 0.0 50 15 13.79 63.8 Example−0.5 — 31 0.0 50 15 14.5 64.5 Example +0.0 +0.0 31 0.0 50 15 15 65Example +0.25 +0.25 31 0.0 50 15 15.25 65.2 Comparative — +0.5 31 1.1150 15 15.5 65.5 example Comparative — +6.5 31 1.67 50 15 21.5 71.5example Comparative — +17.5 31 1.8 50 15 32.5 82.5 example Comparative —+25.5 31 3.72 50 15 40.5 90.5 example Comparative — +34.5 31 6.73 50 1549.5 99.5 example

FIG. 10 shows a relationship between the depth (−ΔDx) of the depression12B5 (13B5) of the lens film 12A or the like according to the foregoingexamples and the amount of warpage in the left side of the figure, andshows a relation between the thickness ΔDy of the skirt layer 112-5 ofthe lens film 112 according to the foregoing comparative examples andthe amount of warpage in the right side of the figure.

From FIG. 10, it was found that in the examples, the amount of warpageof the lens film 12A or the like was 0 regardless of the depth of thedepression 12B5 (13B5) including that the transparent base 12A1 (13A1)was in contact with the valley 12A3 (13A3). Therefore, in the examples,there is no possibility that Newton rings, flaws and the like aregenerated, the display quality of the display apparatus 1 is enormouslyfavorable, and thus the examples are enormously suitable for mobileusage.

Meanwhile, it was found that in the comparative examples, the amount ofwarpage of the lens film 112 was extremely large, and even if the skirtlayer 112-5 slightly existed, the amount of warpage of the lens film 112was drastically increased. That is, it was found that regarding theamount of warpage, a discontinuity existed depending on the presence ofthe skirt layer 112-5. Therefore, in the comparative examples, there isan enormous possibility that Newton rings, flaws and the like aregenerated, the display quality of the display apparatus 1 is easilylowered, and thus the comparative examples are not suitable for mobileusage.

Table 2 shows relative luminance ratios of the lens film 12A or the likewith the depth (−ΔDx) of −4.31 μm, −3.13 μm, −2.46 μm, −2.04 μm, or−1.21 μm where luminance of the lens film 12A or the like was 1 when thedepth (−ΔDx) of the depression 12B5 (13B5) was +0.0 μm. For reference,curvature radius of the curved face 12B6 (13B6) corresponding to thedepth (−ΔDx) of the depression 12B5 (13B5) are shown.

TABLE 2 Depth of depression Curvature Relative (−ΔDx (μm)) radius (μm)luminance ratio −4.31 30 0.998 −3.13 40 1.0245 −2.46 50 1.0246 −2.04 601.0270 −1.21 100 1.0400 0 10000 1

Light luminance outputted through the lens film 12A or the like wasmeasured by, for example, a color luminance meter 300 as shown in FIG.11. The color luminance meter 300 is fixed on a support section 320which is fixed on a level block 310 and extends in the directionperpendicular to the level block 310 with an aperture 300A for takinglight downward. By taking in light outputted from a backlight unit 330placed on the level block 310 from the aperture 300A, luminance of thelight is measured. The lens film 12A or the like was placed on thebacklight unit 330, and luminance when the backlight unit 330 was turnedon was measured. Next, the lens film 12A or the like was not placed onthe backlight unit 330, and luminance when the backlight unit 330 wasturned on was measured. Thereby, the relative luminance ratio wasobtained.

From Table 2, it was found that when the depth ΔDx of the depression12B5 (13B5) was deepened, a range where the relative luminance ratio waslarger than 1 existed. Therefore, by setting the depth (−ΔDx) of thedepression 12B5 (13B5) within the range, the amount of warpage generatedin the lens film 12A or the like could be largely decreased, inaddition, the front luminance could be improved.

In reality, the relative luminance ratio is changed according to thesize of the curvature radius. However, the size of the curvature radiuswhen the relative luminance ratio is larger than 1 is changed accordingto the width (pitch) in the arrangement direction of the pole prism 12B2(13B2), the depth D3 of the valley 12B3 (13B3), and the angle of the top(apex angle) of the pole prism 12B2 (13B2). Therefore, the depth (−ΔDx)of the depression 12B5 (13B5) with which the relative luminance ratiobecomes larger than 1 is difficult to be determined categorically. As acombination frequently used practically, the depth (−ΔDx) of thedepression 12B5 (13B5) with which the relative luminance ratio becomeslarger than 1 is smaller than 0 μm, and about −4 μm or more, consideringthat the depth D3 of the valley 12B3 (13B3) is almost half of the width(pitch) in the arrangement direction of the pole prism 12B2 (13B2), andthe angle of the top (apex angle) of the pole prism 12B2 (13B2) is about90 deg.

Table 3 shows the amount of warpage when the transparent base 12A1 orthe like of the lens film 12A or the like according to the examples wasan existing typical thickness (50 μm) or less, and the amount of warpagewhen the transparent base 122-1 of the lens film 112 according to thecomparative examples was an existing typical thickness (50 μm) or more.In Table 3, when the depression 12B5 (13B5) was provided, D1/D2 was usedas a thickness ratio. When the depth (−ΔDx) was +0.0 μm, +0.25 μm, and+0.28 μm, and when the skirt layer 112-5 existed, D3/D2 was used as athickness ratio.

TABLE 3 Amount of Pitch D2 D1 D3 H D1/D2 D3/D2 −ΔDx ΔDy warpage (μm)(μm) (μm) (μm) (μm) (μm) (μm) (μm) (μm) (mm) Example a 34 25 15.8 16.141.1 — 0.64 — +0.28 0.0 Example b 19 25 8.6 8.1 33.1 0.34 — −0.5 — 0.0Example c 34 25 15.8 14.8 39.8 0.63 — −1.0 — 0.0 Example d 50 25 23.322.8 47.8 1.02 — −0.5 — 0.0 Example e 34 50 15.8 15.3 65.3 0.32 — −0.5 —0.0 Example f 31 50 15 14.5 64.5 0.3  — −0.5 — 0.0 Example g 31 50 15 1565.0 — 0.3  +0.0 +0.0 0.0 Example h 34 50 15.8 16.1 65.1 — 0.33 +0.25+0.25 0.0 Comparative 24 50 11 13 63.0 — 0.26 — +2.0 1.9 example IComparative 50 125 25 30 155 — 0.24 — +5.0 0.4 example k

From Table 3, it was found that in Comparative example i in which thethickness D2 of the transparent base 112-1 was an existing typicalthickness (50 μm), and the thickness ΔDy of the skirt layer 112-5 was+2.0 μm, the large warpage was generated. Therefore, in the past, todecrease the warpage of the lens film 112, the thickness D2 of thetransparent base 112-1 was thick as in Comparative example k.

Meanwhile, in the examples, by practically eliminating the skirt layerby setting the thickness ΔDy of the skirt layer to +0.25 μm as inExample h, or by totally eliminating the skirt layer by setting thethickness ΔDy of the skirt layer to +0.0 μm as in Example g, the warpagecould be eliminated without making the thickness D2 of the transparentbase 12A1 (13A1) thin. Further, for example, by setting the depth (−ΔDx)of the depression 12B5 (13B5) to −0.5 μm as in Example for Example e,for example, the warpage could be eliminated without making thethickness D2 of the transparent base 12B1 (13B1) thick.

Further, in the examples, for example, as in Examples b, c, and d, byproviding the depression 12B5 (13B5) and setting the thickness D2 of thetransparent base 12B1 (13B1) thinner than the existing thickness (25μm), the warpage could be eliminated. Then, in Example d, height H ofthe lens film 12B (13B) was lower than that of the existing height, andthe height D3 of the pole prism 12B2 (13B2) and the pitch of the poleprism 12B2 (13B2) were increased. Therefore, the front luminance couldbe increased without increasing the height H of the lens film 12B (13B)than the existing height. Further, in Example b, since the height D3 ofthe pole prism 12A2 or the like and the pitch of the pole prism 12B2(13B2) were decreased, the lens film 12B (13B) could be thinner.

Further, in the examples, for example, as in Example a, by practicallyeliminating the skirt layer by setting the thickness ΔDy of the skirtlayer to +0.28 μm and setting the thickness D2 of the transparent base12A1 (13A1) thinner than the existing thickness (25 μm), the warpagecould be eliminated.

The foregoing results will be summarized in view from the ratios (D1/D2,D3/D2). By adjusting D1, D2, and D3 to satisfy D1/D2≧0.30 and D3/D2≧0.30and practically or totally eliminating the skirt layer, and further byproviding the depression 12B5 (13B5), it is possible to make the totalthickness of the lens film 12A or the like thin without generatingwarpage, and further to increase the front luminance.

While the invention has been described with reference to the embodimentand the examples, the invention is not limited to the embodiment and thelike, and various modifications may be made.

For example, in the foregoing embodiment and the like, the lens film 12Aor the like respectively has the triangle pole-shaped pole prism 12A2 orthe like. For example, the lens film 12A or the like may have anaspherical microlens.

Further, in the foregoing embodiment and the like, the lens film 12A orthe like has a condensing function. However, the lens film 12A or thelike also has a diffusion function. In this case, micro projections maybe provided on the rear face of the lens film 12A or the like, or therear face of the lens film 12A or the like may be coated with adiffusion material. Otherwise, the lens film 12A or the like itself maycontain a diffusion material. Otherwise, a diffusion sheet or adiffusion plate may be glued on the surface of the lens film 12A or thelike.

Further, in the foregoing embodiment and the like, the lens film 12A orthe like is respectively arranged so that light of the light source 11enters from the transparent base 12A1 or the like side. However, it ispossible that in another display apparatus, the lens film 12A or thelike may be arranged so that light of the light source enters from theside opposite to the transparent base 12A1 or the like, that is, fromthe pole prism 12A2 or the like side.

Further, in the foregoing embodiment and the like, by adjusting thethickness of the hardening resin P dropped on the transparent base S bythe resin supply device 33 to a given thickness by the film thicknessadjustment device 34, the transparent base S is coated with the uncuredhardening resin P. However, the uncured hardening resin P may bearranged on the transparent base S by other method. For example, thetransparent base S previously coated with the uncured hardening resin Pmay be provided in the unwinding device 31. Otherwise, it is possiblethat the surface of the forming roll 35C is previously coated with theuncured hardening resin P, the resultant is pressed by the pressure roll35A, and thereby the uncured hardening resin P is in contact with thetransparent base S. Otherwise, by providing a pool of the uncuredhardening resin P by dropping the uncured hardening resin P in acone-shaped region formed between the surface of the forming roll 35Cand the surface of the transparent base S, the transparent base S may becoated with the uncured hardening resin P.

In the foregoing embodiment and the like, the structure of the displayapparatus 1 has been concretely described. However, it is not necessaryto provide all layers. In addition, other layer (for example, reflectivepolarizing plate) may be provided. That is, various selections may bemade according to the usage and the purpose.

Further, in the foregoing embodiment and the like, the active matrixtype display apparatus 1 has been described. However, the invention canbe applied to a simple matrix-driven display apparatus.

Further, in the foregoing embodiment and the like, the case that theillumination system 10 is an edge-light type has been described.However, the illumination system may be other type such as a subjacenttype. Further, in the foregoing embodiment and the like, the liquidcrystal display apparatus 1 has been described. However, it is needlessto say that the invention can be applied to display apparatusesutilizing other principle.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alternations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. An optical sheet having pole prisms made of a hardening resinarranged along an extending direction on a transparent base made of aflexible material, wherein the transparent base is in contact with avalley between the pole prisms adjacent to each other.
 2. The opticalsheet according to claim 1, wherein the transparent base has adepression corresponding to the valley.
 3. The optical sheet accordingto claim 2, wherein the pole prisms have a sloping face extending to aninner wall of the depression.
 4. The optical sheet according to claim 2,wherein the transparent base has a convex curved face between thevalleys adjacent to each other.
 5. The optical sheet according to claim2, wherein the depression has a depth to an extent that no whitening iscaused at a peripheral portion of the depression of the transparentbase.
 6. The optical sheet according to claim 1, wherein where a depthof the valley is D1 and a thickness of the transparent base is D2, D1and D2 satisfy the following relation:0.3≦D1/D2.
 7. The optical sheet according to claim 1, wherein where athickness of the transparent base is D2 and a height of the pole prismis D3, D2 and D3 satisfy the following relation:0.3≦D3/D2.
 8. A method for producing an optical sheet comprising thesteps of: arranging an uncured hardening resin on a transparent basemade of a flexible material; pressing a mother die having projectionsonto the hardening resin, and pressing tops of the projections onto thetransparent base until the tops of the projections are in contact withthe transparent base; forming the hardening resin by curing thehardening resin in a state that the projections are pressed onto thetransparent base; and peeling the formed hardening resin from the motherdie together with the transparent base.
 9. The method for producing anoptical sheet according to claim 8, wherein the projections are pressedonto the transparent base until depressions are formed in thetransparent base.
 10. The method for producing an optical sheetaccording to claim 8, wherein tops of the projections protrude towardthe transparent base side more than a surface where no projections areformed of the mother die.
 11. A display apparatus comprising: a panel; alight source emitting light for illuminating the panel; and one or aplurality of optical sheets provided between the panel and the lightsource, wherein the optical sheet is structured in a manner that poleprisms made of a hardening resin are arranged along an extendingdirection on a transparent base made of a flexible material, and thetransparent base is in contact with a valley between the pole prismsadjacent to each other.
 12. The display apparatus according to claim 11comprising: a plurality of optical sheets, wherein each of the opticalsheets is arranged so that extending directions of the pole prismsthereof cross each other.
 13. The display apparatus according to claim12, wherein each of the optical sheets is arranged so that light of thelight source enters each of the optical sheets from a transparent baseside.
 14. The display apparatus according to claim 11 comprising: anoptical sheet, wherein the optical sheet is arranged so that light ofthe light source enters the optical sheet from a pole prism side. 15.The display apparatus according to claim 11, wherein the optical sheethas a diffusion function in addition to a condensing function.